While December is not normally the time of year one is trying to come up with strategies to “beat the heat,” it is something that may be on our minds come next summer, so now is a good time to start researching and considering your options. Much focus is placed on hydration for athletes, especially when competing in hot and humid climates. Loosing as little as 2 percent of your body mass via sweat and expired air can result in a significant decrease in endurance capacity. One of the approaches recommended by some top-level coaches is glycerol-loading 5, 6. This idea intrigued me, so I hit the research to dig a little deeper.

Glycerine is the backbone of a triglyceride (fat) molecule. When the fatty acids are stripped off, a glycerol is formed. It is considered to be completely safe because it is a natural metabolite; breaking down into carbon dioxide and water, or glucose. In all the studies I read, there were no documented adverse physiological or biochemical effects related to the ingestion of glycerol.

While most studies did not observe any significant changes in heart rate, maximal oxygen utilization, cardiac output, or lactate accumulation from the ingestion of a glycerol solution, they did find a consistent decreased rate of perceived exertion, and increased plasma volume. Not every study found prolonged time to fatigue, but most did, and one recent study, using a 30-mile mountain bike race (three loops of 10 miles each) in hot and humid conditions, found that the glycerol group completed the 3rd loop five minutes faster than the water group 1. Had this been a longer event, such as a marathon or Ironman-distance triathlon, five minutes for 10 miles could really add up.

One theory for performance improvements is that the glycerol, which can be easily converted to glucose in the liver, was being used as a fuel during activity. While Terblanche et. al. 3 found this to be true in rats, Kavouras et. al. cites three separate studies with humans where there were no changes in plasma glucose levels during activity, indicating glycerol was not an energy substrate 4.

Research involving sedentary individuals showed a definitive increase in hydration following ingestion of a glycerol solution 2. Three different doses (0.5, 1.0, and 1.5 g/kg body weight) all increased water retention after the second hour, and reduced total urine output over a 4-hour period. The smaller dose was deemed “insignificant,” with the later two having results similar to each other, which seems to indicate more does not equate to better; there is a plateau point.

So where does one get their hands on some glycerol? Good question. I found reference to three different companies that were distributors of glycerol marketed toward athletes, one of which was sold off by its parent company for unrelated reasons, and two of which apparently no longer carry it. Tom Rogers 5 refers to using “drug store glycerine” in a 4:1 ratio with water. There is one product I was able to find carried by Hammer Nutrition that contains glycerol. It is called Liquid Endurance, but it contains other ingredients, and makes claims beyond the scope of this article.

As with anything we put in our bodies, there are some downsides to this approach. Some athletes have reported gastro-intestinal distress 6, so if you think you might want to try this, you’ll need to keep that in mind and plan accordingly. Another adverse effect is a two to three pound weight gain (we are storing more water after all) that may leave some feeling heavy, but this is no different than the feeling carbohydrate loading would create. Just remember, don’t try it for the first time on race day; train like you race, and finish strong!